On the Wikipedia pagehttps://en.wikipedia.org/wiki/MACRO-10the example code has this"SEARCH UUOSYM ; Make UUO symbol names available"in the middle of the *original* FORTRAN 77 code for "Colossal Cave Adventure 550" there is this comment "if uuotime or uuodate is..." This program was written in 1978 for a PDP10 machine.

On page C-14 of the DEC publication, "decsystem10 MACRO ASSEMBLER REFERENCE MANUALAA-C780C-TBApril 1978OPERATING SYSTEM & VERSION: TOPS-10, Version 6.03SOFTWARE VERSION: MACRO-10, Version 53"it says,"MACRO-DEFINED MNEMONICSC.6 F40 UUO MNEMONICSTable C-10 shows mnemonics that are defined only if MACRO is assembledwith the F10 switch on. These mnemonics generate UUOs, which arehandled properly if the program is running under control of the FORSEobject-time system."